I knew that it was possible to spy on CRT displays due to the signals they radiate, but apparently that is a problem with HDMI too.
Here a very interesting write up on how to extract frames from leaked RF from HDMI cables and using said RF to transmit a webcam stream even: https://www.windytan.com/2023/02/using-hdmi-radio-interference-for-high.html
Here a example of someone using HDMI RF to transmit LoRa signals: https://www.youtube.com/watch?v=HDbdAZd6cLw
This makes for a interesting attack vector for locating a user, if said user clicks on a video (or even a gif) that crafts LoRa frames to radiate from his HDMI and there is for example a Meshtastic receiver near by that relays those frames into a wider network.
There are ways to migrate this issue, for example using the encrypted version of HDMI usually used to enforce content copyright protection, or using a fiber optic HDMI cable (by now they are almost as cheap as the copper ones and are not restricted to a max lenght of 5m).
Fun fact: before superheterodyne radios were invented, you needed a license to operate a radio including just to plug it in and tune it.
The reason is simple regenerative radios back In the day were also transmitting a small amount of signal back when they were receiving a station. As a result, at least in the US you needed a radio operator’s license to listen to a radio since you were technically transmitting.
Super heterodyne radios fixed this though by having extremely levels of sensitivity and basically now backfeed signal transmitted.
I love seeing mentions of superHets in the wild. Back in my day we sparked car batteries across a measured loop of wire!